Preparation of 2&#39;-fluoro-2&#39;-alkyl-substituted or other optionally substituted ribofuranosyl pyrimidines and purines and their derivatives

ABSTRACT

The present invention provides (i) processes for preparing a 2′-deoxy-2′-fluoro-2′-methyl-D-ribonolactone derivatives, (ii) conversion of intermediate lactones to nucleosides with potent anti-HCV activity, and their analogues, and (iii) methods to prepare the anti-HCV nucleosides containing the 2′-deoxy-2′-fluoro-2′-C-methyl-β-D-ribofuranosyl nucleosides from a preformed, preferably naturally-occurring, nucleoside.

CLAIM TO PRIORITY

This application a continuation of U.S. patent application Ser. No.11/225,425, filed Sep. 13, 2005, which claims the benefit of ProvisionalPatent Application Ser. No. 60/609,783, filed Sep. 14, 2004, ProvisionalPatent Application Ser. No. 60/610,035, filed Sep. 15, 2004, andProvisional Patent Application Ser. No. 60/666,230, filed Mar. 29, 2005.The entire contents of all of the above-mentioned applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention provides (i) processes for preparing a2-deoxy-2-fluoro-2-methyl-D-ribonolactone derivatives, (ii) conversionof intermediate lactones to nucleosides with potent anti-HCV activity,and their analogues, and (iii) methods to prepare the anti-HCVnucleosides containing the2′-deoxy-2′-fluoro-2′-C-methyl-β-D-ribofuranosyl nucleosides from apreformed, preferably naturally-occurring, nucleoside.

BACKGROUND OF THE INVENTION

HCV infection has reached epidemic levels worldwide, and has tragiceffects on the infected patients. Presently there is no effectivetreatment for this infection and the only drugs available for treatmentof chronic hepatitis C are various forms of alpha interferon (IFN-a),either alone or in combination with ribavirin. However, the therapeuticvalue of these treatments has been compromised largely due to adverseeffects, which highlights the need for development of additional optionsfor treatment.

HCV is a small, enveloped virus in the Flaviviridae family, with apositive single-stranded RNA genome of ˜9.6 kb within the nucleocapsid.The genome contains a single open reading frame (ORF) encoding apolyprotein of just over 3,000 amino acids, which is cleaved to generatethe mature structural and nonstructural viral proteins. ORF is flankedby 5′ and 3′ non-translated regions (NTRs) of a few hundred nucleotidesin length, which are important for RNA translation and replication. Thetranslated polyprotein contains the structural core (C) and envelopeproteins (E1, E2, p7) at the N-terminus, followed by the nonstructuralproteins (NS2, NS3, NS4A, NS4B, NS5A, NS5B). The mature structuralproteins are generated via cleavage by the host signal peptidase. Thejunction between NS2 and NS3 is autocatalytically cleaved by the NS2/NS3protease, while the remaining four junctions are cleaved by theN-terminal serine protease domain of NS3 complexed with NS4A. The NS3protein also contains the NTP-dependent helicase activity which unwindsduplex RNA during replication. The NS5B protein possesses RNA-dependentRNA polymerase (RDRP) activity, which is essential for viralreplication. Unlike HBV or HIV, no DNA is involved in the replication ofHCV.

U.S. Patent Publication (US 2005/0009737 A1) discloses that1-(2-deoxy-2-fluoro-2-C-methyl-β-D-ribofuranosyl)cytosine (14) is apotent and selective anti-HCV agent. Previously known syntheticprocedures (Schemes 1-3) for this compound are quite inefficient, withvery low overall yields and are not amendable to large-scale.

Previously known methods for the preparation of(2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleosides, and its analogues,from D-xylose, cytidine, or uridine employed DAST or Deoxofluor® for thekey fluorination reaction. However, DAST and Deoxofluor® are expensive,hazardous for industrial synthesis, and provide often unreliableresults. Therefore, these alkylaminosulfur trifluorides are not suitablefor industrial production.

As a part of an effort to find better fluorination conditions, it hasbeen discovered that opening of a cyclic sulfate withnon-alkylaminosulfur trifluoride fluorinating agents is an excellent wayto synthesize the anti-HCV nucleoside,(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine. In addition, it wasdiscovered that this novel synthetic route can be adopted to othernucleosides including the anti-HCV nucleoside,D-2-deoxy-2-fluoro-cytidine (Devos, et al, U.S. Pat. No. 6,660,721),anti-HBV nucleosides, D andL-2′,3′-didehydro-2′,3′-dideoxy-2′-fluoro-nucleosides (Schinazi, et al,U.S. Pat. No. 6,348,587) (I and II, FIG. 3) as well as other2′-substituted nucleosides such as D- and L-FMAU (Su, et al., J Med.Chem, 1986, 29, 151-154; Chu, et al., U.S. Pat. No. 6,512,107).

What is needed is a novel and cost effective process for the synthesisof 2′-C-alkyl-2′-deoxy-2′-substituted-D-ribopyranosyl nucleosides thathave activity against HCV.

SUMMARY OF INVENTION

The present invention as disclosed herein relates to variousintermediates and synthetic methods for the preparation of compounds ofgeneral formulas [I] and [II],

wherein

-   -   X is halogen (F, Cl, Br),    -   Y is N or CH,    -   Z is halogen, OH, OR′ SH, SR′, NH₂, NHR′, or R′    -   R² is alkyl of C₁-C₃, vinyl, or ethynyl;    -   R^(3′) and R^(5′) can be same or different H, alkyl, aralkyl,        acyl, cyclic acetal such as 2′,3′-O-isopropylidene or        2′,3-O-benzylidene, or 2′,3′-cyclic carbonate.    -   R², R⁴, and R⁵ are independently H, halogen including F, Cl, Br,        I, OH, OR′, SH, SR′, N₃, NH₂, NHR′, NR′₂, NHC(O)OR′, lower alkyl        of C₁-C₆, halogenated (F, Cl, Br, I) lower alkyl of C₁-C₆ such        as CF₃ and CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH═CH₂,        halogenated (F, Cl, Br, I) lower alkenyl of C₂-C₆ such as        CH═CHCl, CH═CHBr and CH═CHI, lower alkynyl of C₂-C₆ such as        C═CH, halogenated (F, Cl, Br, I) lower alkynyl of C₂-C₆, lower        alkoxy of C₁-C₆ such as CH₂OH and CH₂CH₂OH, halogenated (F, Cl,        Br, I) lower alkoxy of C₁C₆, CO₂H, CO₂R′, CONH₂, CONHR′, CONR′₂,        CH═CHCO₂H, CH═CHCO₂R′; and,    -   R′ is an optionally substituted alkyl or acyl of C₁-C₁₂        (particularly when the alkyl is an amino acid residue),        cycloalkyl, optionally substituted alkynyl of C₂-C₆, optionally        substituted lower alkenyl of C₂-C₆, or optionally substituted        acyl.

DETAILED DESCRIPTION

Presently no preventive means against Flaviviridae, including hepatitisC virus (HCV), Dengue virus (DENV), West Nile virus (WNV) or YellowFever virus (YFV), infection is available. The only approved therapiesare for treatment of HCV infection with alpha interferon alone or incombination with the nucleoside ribavirin, but the therapeutic value ofthese treatments has been compromised largely due to adverse effects. Itwas recently discovered that a group of nucleosides, including2′-deoxy-2′-fluoro-2′-C-methylcytidine, exhibit potent and selectiveactivity against replication of HCV in a replicon system. However, thedifficulty of chemical synthesis of this and analogous nucleosidesimpedes further biophysical, biochemical, pharmacological evaluationsmandatory for development of clinical drugs for treatment ofFlaviviridae infection.

The present invention provides an efficient preparation of nucleosidesand intermediates containing the2-deoxy-2-fluoro-2-C-methyl-D-ribofuranosyl moiety.

DEFINITIONS

The term “independently” is used herein to indicate that the variable,which is independently applied, varies independently from application toapplication. Thus, in a compound such as R^(a)XYR^(a), wherein R^(a) is“independently carbon or nitrogen”, both R^(a) can be carbon, both R^(a)can be nitrogen, or one R^(a) can be carbon and the other R^(a)nitrogen.

As used herein, the terms “enantiomerically pure” or “enantiomericallyenriched” refers to a nucleoside composition that comprises at leastapproximately 95%, and preferably approximately 97%, 98%, 99% or 100% ofa single enantiomer of that nucleoside.

As used herein, the term “substantially free of” or “substantially inthe absence of” refers to a nucleoside composition that includes atleast 85 or 90% by weight, preferably 95% to 98% by weight, and evenmore preferably 99% to 100% by weight, of the designated enantiomer ofthat nucleoside. In a preferred embodiment, in the methods and compoundsof this invention, the compounds are substantially free of enantiomers

The term “alkyl,” as used herein, unless otherwise specified, refers toa saturated straight or branched hydrocarbon chain of typically C₁ toC₁₀, and specifically includes methyl, ethyl, propyl, isopropyl, butyl,isobutyl, t-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl,cyclohexyl, cyclohexylmethyl, 3-methylpentyl, 2,2-dimethylbutyl, and2,3-dimethylbutyl, and the like. The term includes both substituted andunsubstituted alkyl groups. Alkyl groups can be optionally substitutedwith one or more moieties selected from the group consisting ofhydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano,sulfonic acid, sulfate, phosphonic acid, phosphate, or phosphonate. Oneor more of the hydrogen atoms attached to carbon atom on alkyl may bereplaced by one or more halogen atoms, e.g. fluorine or chlorine orboth, such as trifluoromethyl, difluoromethyl, fluorochloromethyl, andthe like. The hydrocarbon chain may also be interrupted by a heteroatom,such as N, O or S.

The term “lower alkyl,” as used herein, and unless otherwise specified,refers to a C₁ to C₄ saturated straight or branched alkyl group,including both substituted and unsubstituted forms as defined above.Unless otherwise specifically stated in this application, when alkyl isa suitable moiety, lower alkyl is preferred. Similarly, when alkyl orlower alkyl is a suitable moiety, unsubstituted alkyl or lower alkyl ispreferred.

The term “cycloalkyl”, as used herein, unless otherwise specified,refers to a saturated hydrocarbon ring having 3-8 carbon atoms,preferably, 3-6 carbon atoms, such as cyclopropyl, cyclobutyl,cyclopentyl and cyclohexyl. The cycloalkyl group may also be substitutedon the ring by an alkyl group, such as cyclopropylmethyl and the like.

The terms “alkylamino” or “arylamino” refer to an amino group that hasone or two alkyl or aryl substituents, respectively.

The term “protected,” as used herein and unless otherwise defined,refers to a group that is added to an oxygen, nitrogen, or phosphorusatom to prevent its further reaction or for other purposes. A widevariety of oxygen and nitrogen protecting groups are known to thoseskilled in the art of organic synthesis. Non-limiting examples include:C(O)-alkyl, C(O)Ph, C(O)aryl, CH₃, CH₂-alkyl, CH₂-alkenyl, CH₂Ph,CH₂-aryl, CH₂O-alkyl, CH₂O-aryl, SO₂-alkyl, SO₂-aryl,tert-butyldimethylsilyl, tert-butyldiphenylsilyl, and1,3-(1,1,3,3-tetraisopropyldisiloxanylidene).

The term “aryl,” as used herein, and unless otherwise specified, refersto phenyl, biphenyl, or naphthyl, and preferably phenyl. The termincludes both substituted and unsubstituted moieties. The aryl group canbe substituted with one or more substituents, including, but not limitedto hydroxyl, halo, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro,cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, orphosphonate, either unprotected, or protected as necessary, as known tothose skilled in the art, for example, as taught in T. W. Greene and P.G. M. Wuts, “Protective Groups in Organic Synthesis,” 3rd ed., JohnWiley & Sons, 1999.

The terms “alkaryl” or “alkylaryl” refer to an alkyl group with an arylsubstituent. The terms “aralkyl” or “arylalkyl” refer to an aryl groupwith an alkyl substituent, as for example, benzyl.

The term “halo,” as used herein, includes chloro, bromo, iodo andfluoro.

The term “acyl ester” or “O-linked ester” refers to a carboxylic acidester of the formula C(O)R′ in which the non-carbonyl moiety of theester group, R′, is a straight or branched alkyl, or cycloalkyl or loweralkyl, alkoxyalkyl including methoxymethyl, aralkyl including benzyl,aryloxyalkyl such as phenoxymethyl, aryl including phenyl optionallysubstituted with halogen (F, Cl, Br, I), C₁ to C₄ alkyl or C₁ to C₄alkoxy, sulfonate esters such as alkyl or aralkyl sulphonyl includingmethanesulfonyl, the mono, di or triphosphate ester, trityl ormonomethoxytrityl, substituted benzyl, trialkylsilyl (e.g.dimethyl-t-butyl silyl) or diphenylmethylsilyl. Aryl groups in theesters optimally include a phenyl group.

The term “acyl” refers to a group of the formula R″C(O)—, wherein R″ isa straight or branched alkyl, or cycloalkyl, amino acid, aryl includingphenyl, alkylaryl, aralkyl including benzyl, alkoxyalkyl includingmethoxymethyl, aryloxyalkyl such as phenoxymethyl; or substituted alkyl(including lower alkyl), aryl including phenyl optionally substitutedwith chloro, bromo, fluoro, iodo, C₁ to C₄ alkyl or C₁ to C₄ alkoxy,sulfonate esters such as alkyl or aralkyl sulphonyl includingmethanesulfonyl, the mono, di or triphosphate ester, trityl ormonomethoxy-trityl, substituted benzyl, alkaryl, aralkyl includingbenzyl, alkoxyalkyl including methoxymethyl, aryloxyalkyl such asphenoxymethyl. Aryl groups in the esters optimally comprise a phenylgroup. In particular, acyl groups include acetyl, trifluoroacetyl,methylacetyl, cyclopropylacetyl, cyclopropyl carboxy, propionyl,butyryl, isobutyryl, hexanoyl, heptanoyl, octanoyl, neo-heptanoyl,phenylacetyl, 2-acetoxy-2-phenylacetyl, diphenylacetyl,α-methoxy-α-trifluoromethyl-phenylacetyl, bromoacetyl,2-nitro-benzeneacetyl, 4-chloro-benzeneacetyl,2-chloro-2,2-diphenylacetyl, 2-chloro-2-phenylacetyl, trimethylacetyl,chlorodifluoroacetyl, perfluoroacetyl, fluoroacetyl,bromodifluoroacetyl, methoxyacetyl, 2-thiopheneacetyl,chlorosulfonylacetyl, 3-methoxyphenylacetyl, phenoxyacetyl,tert-butylacetyl, trichloroacetyl, monochloro-acetyl, dichloroacetyl,7H-dodecafluoro-heptanoyl, perfluoro-heptanoyl,7H-dodeca-fluoroheptanoyl, 7-chlorododecafluoro-heptanoyl,7-chloro-dodecafluoro-heptanoyl, 7H-dodecafluoroheptanoyl,7H-dodeca-fluoroheptanoyl, nona-fluoro-3,6-dioxa-heptanoyl,nonafluoro-3,6-dioxaheptanoyl, perfluoroheptanoyl, methoxybenzoyl,methyl 3-amino-5-phenylthiophene-2-carboxyl,3,6-dichloro-2-methoxy-benzoyl, 4-(1,1,2,2-tetrafluoro-ethoxy)-benzoyl,2-bromo-propionyl, omega-aminocapryl, decanoyl, n-pentadecanoyl,stearyl, 3-cyclopentyl-propionyl, 1-benzene-carboxyl, O-acetylmandelyl,pivaloyl acetyl, 1-adamantane-carboxyl, cyclohexane-carboxyl,2,6-pyridinedicarboxyl, cyclopropane-carboxyl, cyclobutane-carboxyl,perfluorocyclohexyl carboxyl, 4-methylbenzoyl, chloromethyl isoxazolylcarbonyl, perfluorocyclohexyl carboxyl, crotonyl,1-methyl-1H-indazole-3-carbonyl, 2-propenyl, isovaleryl,1-pyrrolidinecarbonyl, 4-phenylbenzoyl. When the term acyl is used, itis meant to be a specific and independent disclosure of acetyl,trifluoroacetyl, methylacetyl, cyclopropylacetyl, propionyl, butyryl,isobutyryl, hexanoyl, heptanoyl, octanoyl, neo-heptanoyl, phenylacetyl,diphenylacetyl, ct-trifluoromethyl-phenylacetyl, bromoacetyl,4-chloro-benzeneacetyl, 2-chloro-2,2-diphenylacetyl,2-chloro-2-phenylacetyl, trimethylacetyl, chlorodifluoroacetyl,perfluoroacetyl, fluoroacetyl, bromodifluoroacetyl, 2-thiopheneacetyl,tert-butylacetyl, trichloroacetyl, monochloro-acetyl, dichloroacetyl,methoxybenzoyl, 2-bromo-propionyl, decanoyl, n-pentadecanoyl, stearyl,3-cyclopentyl-propionyl, 1-benzene-carboxyl, pivaloyl acetyl,1-adamantane-carboxyl, cyclohexane-carboxyl, 2,6-pyridinedicarboxyl,cyclopropane-carboxyl, cyclobutane-carboxyl, 4-methylbenzoyl, crotonyl,1-methyl-1H-indazole-3-carbonyl, 2-propenyl, isovaleryl,4-phenylbenzoyl.

The term “lower acyl” refers to an acyl group in which R″, abovedefined, is lower alkyl.

The term “natural nucleic base” and “modified nucleic base” refer to“purine” or “pyrimidine” bases as defined below.

The term “purine” or “pyrimidine” base includes, but is not limited to,adenine, N⁶-alkylpurines, N⁶-acylpurines (wherein acyl is C(O)(alkyl,aryl, alkylaryl, or arylalkyl), N⁶-benzylpurine, N⁶-halopurine,N⁶-vinylpurine, N⁶-acetylenic purine, N⁶-acyl purine, N⁶-hydroxyalkylpurine, N⁶-allylaminopurine, N⁶-thioallyl purine, N⁶-alkylpurines,N²-alkyl-6-thiopurines, thymine, cytosine, 5-fluorocytosine,5-methylcytosine, 6-azapyrimidine, including 6-azacytosine, 2- and/or4-mercaptopyrimidine, uracil, 5-halouracil, including 5-fluorouracil,C⁵-alkylpyrimidines, C⁵-benzylpyrimidines, C⁵-halopyrimidines,C⁵-vinylpyrimidine, C⁵-acetylenic pyrimidine, C⁵-acyl pyrimidine,N⁴-acetylcytosine, N⁴-benzoylcytosine, N⁴-alkyl pyrimidine,C⁵-hydroxyalkyl purine, C⁵-amidopyrimidine, C⁵-cyanopyrimidine,C⁵-iodopyrimidine, C⁶-iodo-pyrimidine, C⁵-Br-vinyl pyrimidine,C⁶-Br-vinyl pyrimidine, C⁵-nitropyrimidine, C⁵-amino-pyrimidine,N²-alkylpurines, N²-alkyl-6-thiopurines, 5-azacytidinyl, 5-azauracilyl,triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, andpyrazolopyrimidinyl. Purine bases include, but are not limited to,guanine, adenine, hypoxanthine, 2,6-diaminopurine, and 6-chloropurine.Functional oxygen and nitrogen groups on the base can be protected asnecessary or desired. Suitable protecting groups are well known to thoseskilled in the art, and include trimethylsilyl, dimethylhexylsilyl,t-butyldimethylsilyl, and t-butyldiphenylsilyl, trityl, alkyl groups,and acyl groups such as acetyl and propionyl, methanesulfonyl, andp-toluenesulfonyl.

The term “amino acid” includes naturally occurring and synthetic α, β γor δ amino acids, and includes but is not limited to, amino acids foundin proteins, i.e. glycine, alanine, valine, leucine, isoleucine,methionine, phenylalanine, tryptophan, proline, serine, threonine,cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine,arginine and histidine. In a preferred embodiment, the amino acid is inthe L-configuration. Alternatively, the amino acid can be a derivativeof alanyl, valinyl, leucinyl, isoleucinyl, prolinyl, phenylalaninyl,tryptophanyl, methioninyl, glycinyl, serinyl, threoninyl, cysteinyl,tyrosinyl, asparaginyl, glutaminyl, aspartoyl, glutaroyl, lysinyl,argininyl, histidinyl, β-alanyl, β-valinyl, β-leucinyl, β-isoleucinyl,β-prolinyl, β-phenylalaninyl, β-tryptophanyl, β-methioninyl, β-glycinyl,β-serinyl, β-threoninyl, β-cysteinyl, β-tyrosinyl, β-asparaginyl,β-glutaminyl, β-aspartoyl, β-glutaroyl, β-lysinyl, β-argininyl orβ-histidinyl. When the term amino acid is used, it is considered to be aspecific and independent disclosure of each of the esters of α, βγ or δglycine, alanine, valine, leucine, isoleucine, methionine,phenylalanine, tryptophan, proline, serine, threonine, cysteine,tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginineand histidine in the D and L-configurations.

The term “pharmaceutically acceptable salt or prodrug” is usedthroughput the specification to describe any pharmaceutically acceptableform (such as an ester, phosphate ester, salt of an ester or a relatedgroup) of a compound which, upon administration to a patient, providesthe active compound. Pharmaceutically acceptable salts include thosederived from pharmaceutically acceptable inorganic or organic bases andacids. Suitable salts include those derived from alkali metals such aspotassium and sodium, alkaline earth metals such as calcium andmagnesium, among numerous other acids well known in the pharmaceuticalart. Pharmaceutically acceptable salts may also be acid addition saltswhen formed with a nitrogen atom. Such salts are derived frompharmaceutically acceptable inorganic or organic acids, such ashydrochloric, sulfuric, phosphoric, acetic, citric, tartaric, and thelike. Pharmaceutically acceptable prodrugs refer to a compound that ismetabolized, for example hydrolyzed or oxidized, in the host to form thecompound of the present invention. Typical examples of prodrugs includecompounds that have biologically labile protecting groups on afunctional moiety of the active compound. Prodrugs include compoundsthat can be oxidized, reduced, aminated, deaminated, hydroxylated,dehydroxylated, hydrolyzed, dehydrolyzed, alkylated, dealkylated,acylated, deacylated, phosphorylated, dephosphorylated to produce theactive compound.

Applicants have developed a novel, practical and efficient process forthe synthesis of 2-C-alkyl-2-deoxy-2-substituted-D-ribofuranosederivatives, the key intermediates to 14 (Scheme 1) and derivatives andanalogues thereof using or without using chiral catalysts. The key stepin the synthesis of 14 is asymmetric conversion of 41 to 42 using chiralcatalysts (Scheme 4). The previous disclosed synthesis of 42 requiredSharpless AD catalysts, such as dihydroquinidine (DHQD) and derivatives.The present invention as disclosed herein relates to the stereoselectivepreparation of 41 to 42 using osmium, osmate or permanganate withoutchiral catalysts. The applicants in this present invention also developa practical and efficient process for the synthesis of 49 from 42 byusing the nucleophilic opening of the cyclic sulfate 50 (Scheme 6) inhighly stereospecific and regioselective manner. The procedure depictedin Schemes 4, 5 and 6 are the current method of choice for preparativesynthesis of 14 and related derivatives.

I. Preparation of the Compounds

(i) Synthesis of the Cyclic Sulfite (IIIa) and Cyclic Sulfate (IIIb)

This invention relates to the process for the preparation of the2′-F-nucleosides and other 2′-substituted nucleosides of the generalformula IB and IB-L- by using the nucleophilic opening of the cyclicsulfite, IIIa (X═SO), sulfate, IIIb (X═SO₂), of the formula, III inhighly stereospecific and regioselective manner, via the lactones of theformula, IV.

Wherein the formula IB, IB-L, III, IV has following specifications:

-   -   R¹ is independently a lower alkyl (C₁-C₆) including, but not        limited to methyl, ethyl, optionally substituted phenyl,        optionally substituted benzyl; alternatively R¹ is a part of        cyclic alkylene including ethylene (—CH₂CH₂—), or trimethylene        (—CH₂CH₂CH₂—) forming cyclic pentyl or cyclic hexanyl group;    -   R², R³ are independently hydrogen, a lower alkyl (C₁-C₆)        including, but not limited to methyl, hydroxymethyl,        methoxymethyl, halomethyl including, but not limited to        fluoromethyl, ethyl, propyl, optionally substituted ethenyl        including, but not limited to vinyl, halovinyl (F—CH═C),        optionally substituted ethynyl including, but not limited to        haloethynyl (F—C≡C), optionally substituted allyl including, but        not limited to haloallyl (FHC═CH—CH₂—);    -   R⁴ is independently hydrogen, aryl including, but not limited to        phenyl, aryl alkyl including, but not limited to benzyl, lower        alkyl including, but not limited to, methyl, ethyl, propyl. Nu        is halogen (F, Cl, Br), N₃, CN, NO₃, CF₃, OR or NR where R is        acyl including, but not limited to acetyl, benzoyl, arylalkyl        including but not limited to benzyl, lower alkyl including, but        not limited to, methyl, ethyl, propyl, CH₂R where R is hydrogen,        lower alkyl including, but not limited to, methyl, ethyl,        propyl;    -   X is SO₂, SO, or CO; and    -   B is a natural or modified nucleic base.        In one embodiment, formula, IB is:

wherein,

-   -   R², R³ are independently hydrogen, a lower alkyl (C₁-C₆)        including, but not limited to methyl, hydroxymethyl,        methoxymethyl, halomethyl including, but not limited to        fluoromethyl, ethyl, propyl, optionally substituted ethenyl        including, but not limited to vinyl, halovinyl (F—CH═C),        optionally substituted ethnyl including, but not limited to        haloethnyl (F—C═C), optionally substituted allyl including, but        not limited to haloallyl (FHC═CH—CH₂—);    -   B is a natural or modified nucleic base.

The present invention as disclosed herein relates to processes for thesynthesis of a compound,2-alkyl-4,5-di-O-protected-2,3-dihydroxy-pentanoic-acid ester of thefollowing general formula 42B, which is the important intermediate inthe synthesis of anti-HCV nucleosides of general formulas [I] and [II](below).

wherein R′, R″=isopropylidene, benzylidene or cyclohexylidene or a like,or a part of cyclic group including ethylene (—CH₂CH₂—), or trimethylene(—CH₂CH₂CH₂—) forming cyclopentyl or cyclohexanyl group, respectively;R′ and R″ can be independently lower alkyl of C₁-C₆, or aryl of C₆-C₂₀),benzyl and other optionally substituted benzyl, trialkylsilyl,t-butyl-dialkylsyl, t-butyldiphenylsilyl, TIPDS, THP, MOM, MEM and otheroptionally ether protecting groups; or H, acetyl, benzoyl and otheroptionally substituted acyl (R′ and R″ are —C(O)—R, wherein R can belower alkyl of C₁-C₆, or aryl of C₆-C₂₀, benzyl or other optionallysubstituted benzyl);

R₁, R₂ are independently hydrogen, aryl (C₆-C₂₀) and a lower alkyl(C₁-C₆) including methyl, hydroxymethyl, methoxymethyl, halomethylincluding fluoromethyl, ethyl, propyl, optionally substituted ethenylincluding vinyl, halovinyl (F—CH═C), optionally substituted ethynylincluding haloethynyl (F—C≡C), optionally substituted allyl includinghaloallyl (FHC═CH—CH₂—); and

R₃ is independently hydrogen, aryl including phenyl, aryl alkylincluding, but not limited to benzyl, lower alkyl (C₁₋₆) includingmethyl, ethyl, or propyl.

The invention as disclosed herein also relates to processes for makingcompounds of the following general formula 49B, which are prepared from2-alkyl-4,5-di-O-protected-2,3-dihydroxy-pentanoic-acid esterderivatives of general formula [42B].

wherein R³ and R⁵ can be independently H, CH₃, Ac, Bz, pivaloyl, or4-nitrobenzoyl, 3-nitrobenzoyl, 2-nitrobenzoyl, 4-chlorobenzoyl,3-chlorobenzoyl, 2-chlorobenzoyl, 4-methylbenzoyl, 3-methylbenzoyl,2-methylbenzoyl, para-phenylbenzoyl, and other optionally substitutedacyl (R³ and R⁵ are —C(O)—R, R can be independently lower alkyl ofC₁-C₆, or aryl of C₆-C₂₀), benzyl, 4-methoxybenzyl and other optionallysubstituted benzyl (R³ and R⁵ can be independently aryl of C₆-C₂₀),trityl, trialkylsilyl, t-butyl-dialkylsyl, t-butyldiphenylsilyl, TIPDS,THP, MOM, MEM and other optionally ether protecting groups (R³ and R⁵can be independently alkyl of C₁-C₁₀), or R³ and R⁵ are linked through—SiR₂—O—SiR₂— or —SiR₂—, wherein R is a lower alkyl group such as Me,Et, n-Pr or i-Pr.

wherein

-   -   X is halogen (F, Cl, Br),    -   Y is N or CH,    -   Z is, halogen, OH, OR′, SH, SR′, NH₂, NHR′, or R′    -   R^(2′) is alkyl of C₁-C₃, vinyl, or ethynyl    -   R^(3′) and R^(5′) can be same or different H, alkyl, aralkyl,        acyl, cyclic acetal such as 2′,3′-O-isopropylidene or        2′,3-O-benzylidene, or 2′,3′-cyclic carbonate.    -   R², R⁴, R⁵ and R⁶ are independently H, halogen including F, Cl,        Br, I, OH, OR′, SH, SR′, N₃, NH₂, NHR′, NR″, NHC(O)OR′, lower        alkyl of C₁-C₆, halogenated (F, Cl, Br, I) lower alkyl of C₁-C₆        such as CF₃ and CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH═CH₂,        halogenated (F, Cl, Br, I) lower alkenyl of C₂-C₆ such as        CH═CHCl, CH═CHBr and CH═CHI, lower alkynyl of C₂-C₆ such as        C═CH, halogenated (F, Cl, Br, I) lower alkynyl of C₂-C₆, lower        alkoxy of C₁-C₆ such as CH₂OH and CH₂CH₂OH, halogenated (F, Cl,        Br, I) lower alkoxy of C₁-C₆, CO₂H, CO₂R′, CONH₂, CONHR′,        CONR′₂, CH═CHCO₂H, CH═CHCO₂R′; and,    -   R′ and R″ are the same or different and are optionally        substituted alkyl of C₁-C₁₂ (particularly when the alkyl is an        amino acid residue), cycloalkyl, optionally substituted alkynyl        of C₂-C₆, optionally substituted lower alkenyl of C₂-C₆, or        optionally substituted acyl.

The reaction of the cyclic sulfate ester, 50 (Scheme 6) withtetraethylammonium fluoride or tetramethylammonium fluoride 51 (Scheme6) quantitatively generated the fluorinated sulfate, in highlystereospecific and regioselective manner. Following acid catalyzedcyclization afforded the 2-fluoro-2-C-methyl-γ-ribonolactone, 53 in highyield. The present invention is based on this discovery and provides aprocess for the preparation of the 2′-deoxy-2′-substituted nucleosides,I and II, using the reactions described herein.

(2S,3R,4R)-4,5-O-alkylidene-2-dimethyl-2,3,4,5-tetrahydroxy-2-methyl-1-pentanoicacid ethyl ester (42B), can be prepared by asymmetric dihydroxylation(AD) or stereoselective dihydroxylation of the Wittig product 41 with orwithout chiral catalysts. Wittig product 41, in turn, can be preparedreadily from the protected (R) glyceraldehyde (Schemes 7, 8), where R¹is independently a lower alkyl (C₁-C₆) including, but not limited tomethyl, ethyl, optionally substituted phenyl, optionally substitutedbenzyl. Or R¹ is a part of cyclic group including ethylene (—CH₂CH₂—),or trimethylene (—CH₂CH₂CH₂—) forming cyclopentyl or cyclohexanyl group,respectively. R², R³ are independently hydrogen, a lower alkyl (C₁-C₆)including, but not limited to methyl, hydroxymethyl, methoxymethyl,halomethyl including, but not limited to fluoromethyl, ethyl, propyl,optionally substituted ethenyl including, but not limited to vinyl,halovinyl (F—CH═C), optionally substituted ethynyl including, but notlimited to haloethynyl (F—C≡C), optionally substituted allyl including,but not limited to haloallyl (FHC═CH—CH₂—); and R⁴ is acyl including,but not limited to acetyl, benzoyl, arylalkyl including but not limitedto benzyl, lower alkyl (C₁₋₁₀) including, but not limited to, methyl,ethyl, propyl, CH₂R where R is hydrogen, lower alkyl (C₁₋₁₀) including,but not limited to, methyl, ethyl, propyl.

The diol (42B) can be converted to the cyclic sulfite (IIIa) bytreatment with thionyl chloride (SOCl₂) in presence of an alkylaminesuch as triethylamine, diisopropyl ethylamine, or pyridine, which canthen be oxidized using the oxidants selected from a first groupconsisting of RuCl₃, KMnO₄, and TEMPO or a combination of the firstgroup and one of the second group consisting of NaIO₄, KIO₄, HIO₄,mCPBA, NaOCl, and oxone. The solvent of this step is selected from oneor more of the group consisting of chloroform, methylene chloride,1,2-dichloroethane, diethyl ether, tetrahydrofuran, benzene, andtoluene, alone or in combination with water. (Gao Y et al J. Am. Chem.Soc. 1988, 110, 7538-7539, Berridge et al J. Org. Chem. 1990, 55,1211-1217). It is also possible that the diol is directly converted tothe cyclic sulfate (IIIb) by treatment with sulfurylchloride, orsulfuryl diimidazole. On the other hand, the diol 42B can be convertedto the cyclic carbonate (IIIc) by treatment with carbonyl diimidazole orcarbonyl dimethoxide (Scheme 8) (Chang, et al Tetrahedron Lett. 1996,37, 3219-3222).

(ii) Synthesis of the Substituted 2-deoxy-D-ribono-γ-lactone, 53B

The cyclic sulfate (IIIb, Scheme 8) can be converted to the fluorinatedsulfate ester of the formula, 51B (Scheme 9), in high yield and withhigh regioselectivity and stereospecificity, by treatment withtetraalkylammonium fluoride including, but not limited totetramethylammonium fluoride (TMAF), tetraethylammonium fluoride (TEAF),or tetrabutylammomnium fluoride (TBAF), or tris(dimethylamino)sulfur(trimethylsilyl)difluoride (TAS-F) (Fuentes J, et al Tetrahedron lett.1998, 39, 7149-7152) in an aprotic polar solvent such as acetone,tetrahydrofuran, N,N-dimethylformamide, or acetonitrile (Scheme 9).Metal fluorides such as silver fluoride (AgF), potassium fluoride (KF),cesium fluoride (CsF), or rubidium fluoride (RbF), can be used alone orwith catalytic amount of tetraalkylammonium fluoride, crown-ether,diglyme, or polyethylene glycol, or other phase transfer catalyst.

The cyclic sulfate (IIIb) can be converted to other 2-substitutedsulfates of the formula MB by treatment with NaBH₄, tetraalkylammoniumchloride, tetraalkylammonium bromide, NaN₃ or LiN₃, NH₄OR, NH₄SCN,CF₃I-tetrakis(dimethylamino)-ethylene (TDAE), and tetraalkylammoniumnitrate (Gao et al J. Am. Chem. Soc. 1988, 110, 7538-7539), KCN,LiCu(R)₂ where R is methyl, ethyl, ethylenyl, or ethnyl. Similarly, thecyclicsulfite (IIIa) can be converted to the substituted ester 52B(Chang et al. Tetrahedron Lett. 1996, 37, 3219-3222). Then compounds ofthe formula 51B and 52B can be converted to the substituted lactones ofthe formula 53B by treatment with an acid in H₂O-containing organicsolvent such as methanol, ethanol, or acetonitrile.

In Formula 53B, R², R³ is independently hydrogen, a lower alkyl (C₁-C₆)including, but not limited to methyl, hydroxymethyl, methoxymethyl,halomethyl including, but not limited to fluoromethyl, ethyl, propyl,optionally substituted ethenyl including, but not limited to vinyl,halovinyl (F—CH═C), optionally substituted ethynyl including, but notlimited to haloethynyl (F—C≡C), optionally substituted allyl including,but not limited to haloallyl (FHC═CH—CH₂—). Nu is halogen (F, Cl, Br),N₃, CN, NO₃, CF₃, SCN, OR or NR₂ where R is acyl including, but notlimited to acetyl, benzoyl, arylalkyl including but not limited tobenzyl, lower alkyl (C₁₋₁₀) including, but not limited to methyl, ethyl,propyl, CH₂R where R is hydrogen, lower alkyl (C₁₋₁₀) including, but notlimited to methyl, ethyl, propyl.

(iii) The Protection of the D-ribono-γ-lactone, 53B

53B can be selectively protected with appropriate protection agents tothe 5-protected lactones of the formula 53C with an appropriate base inan appropriate solvent. The protecting group includes, but is notlimited to the following: trityl, t-butyldimethylsilyl,t-butyldiphenylsilyl, benzyloxymethyl, benzoyl, toluoyl, 4-phenylbenzoyl, 2-, 3-, or 4-nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, othersubstituted benzoyl. The base includes, but is not limited to thefollowing: imidazole, pyridine, 4-(dimethylamino)pyridine,triethyllamine, diisopropylethylamine, 1,4-diazabicyclo[2,2,2]-octane.The solvent includes, but is not limited to the following: pyridine,dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran.

Alternatively, the lactone 53B can be fully protected with appropriateprotection agents with an appropriate base in an appropriate solvent.The protecting group (R⁵, R⁶) includes, but is not limited to thefollowing: methoxymethyl, methoxyethyl, benzyloxymethyl, ethoxymethyl,trityl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl, acylincluding acetyl, pivaloyl, benzoyl, toluoyl, 4-phenyl benzoyl, 2-, 3-,or 4-nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, other substitutedbenzoyl. The base includes, but is not limited to the following list:imidazole, pyridine, 4-(dimethylamino)pyridine, triethyllamine,diisopropylethylamine, 1,4-diazabicyclo[2,2,2]octane. The solventincludes, but is not limited to pyridine, dichloromethane, chloroform,1,2-dichloroethane, tetrahydrofuran (Scheme 10).

(ii) Complexation Directed β-glycosylation

Coupling of 2-deoxy-2-fluoro-2-C-methyl-ribofuranoside (54: Nu=F, R³=Me,R⁵═R⁶=pivaloyl) with silylated 1V⁴-benzoylcytosine in the presence oftrimethylsilyl trifluoromethanesulfonate (TMSOTf) in CHCl₃ gave amixture of α/β-anomers with a ratio of 2/1 in favor of a-isomer.However, β-anomer was obtained as major product (α/β=1/4.9) in the samereaction catalyzed by SnCl₄ under similar conditions. Possiblemechanisms are proposed in Scheme 10A (R⁵ and R⁶ are O-protecting groupsthat can be acyl or silyl or alkyl or aralkyl with C₁₋₂₀). Treatment of54 with silylated N⁴-benzoylcytosine in the presence of TMSOTf in CHCl₃formed an oxonium intermediate 54-i. Silylated base could attack 54-1from up-side to give β-anomer 55B or from bottom to provide α-anomer55B-alpha. Because of stereohinderance at up-side caused by 2-methylgroup, silylated base attacked intermediate 54-i mainly from bottom(less stereohindered side) to afford a mixture of α/β-anomers with aratio of 2/1 in favor of α-anomer. While treatment of 54 with silylatedN⁴-benzoylcytosine in the presence of SnCl₄, a complex 54-ii was formedinstead of oxonium 54-i. Silyated N⁴-benzoylcytosine attacked 54-ii fromless stereohindered up-side to give a mixture of α/β-anomers with aratio of 1/5 in favor of β-anomer.

Compound 54 can be made from the protected lactone of the formula, 49B,which can be reduced with DIBAL-H or lithium tri-tert-butoxyaluminumhydride and other hydride reducing agent to the lactol, which can thenconverted either to the acylate by acylation with acyl halide, or acylanhydride, in presence of an appropriate base in an appropriate solvent.Acyl halide or acyl anhydride includes, but is not limited to thefollowing list: acetic chloride, optionally substituted benzoylchloride, acetic anhydride, optionally substituted benzoyl anhydride.The base includes, but is not limited to the following: imidazole,pyridine, 4-(dimethylamino)pyridine, triethyllamine,diisopropylethylamine, 1,4-diazabicyclo[2,2,2]octane. The solventincludes, but is not limited to the following list: pyridine,dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran.

(iii) Synthesis of the L-nucleosides, IB-L

The processes for the D-series of the formula I and II can be used forpreparation of the L-nucleosides of the formula, IB-L from the(S)-glyceraldehydes (Scheme 11).

(iv) Synthesis of 2-alkyl-4,5-di-O-protected-2,3-dihydroxy-pentanoicacid

Currently, the most preferable procedure for the synthesis ofnucleosides of general structures I and II is the preparation of aderivative of the 2-deoxy-2-fluoro-2-C-methyl-D-ribofuranosyl moiety ofI and II as shown in Scheme 4, Scheme 5 and Scheme 6, above through (i)synthesis of the intermediate, derivatives of2-alkyl-4,5-di-O-protected-2,3-dihydroxy-pentanoic-acid ester of generalstructure I, (ii) conversion of 42B into the 3,5-protected2-deoxy-2-fluoro-2-C-methyl-D-ribono-γ-latone of general structure 49B,and (iii) conversion of 49B into purine and pyrimidine nucleosides ofgeneral structures of I and II. The key step in Scheme 4 is thestereoselective osmium catalyzed dihydroxylation of olefinicintermediate 41 into 42 in the presence of the expensive Sharpless ADcatalyst. Instead of the Sharpless catalyst, if other chiral compoundssuch as L-quinidine are used, the reaction also goes smoothly giving thedesired 42. Kishi et al. have proposed that in OsO₄ dihydroxylation ofallylic alcohol derivatives (esters, ethers, acetals or ketals), themajor course of reaction would occur on the face of the olefinic bondopposite to that of the preexisting hydroxyl or alkoxyl group,(Tetrahedron Lett, 1983, 24, 3943). Some examples are shown in Scheme 12(Tetrahedron Lett, 1983, 24, 3947). In every case, the major productarose from addition of OSO₄ from the anti side of the oxygen on theneighboring secondary carbon. However, stereoselectivity is not highenough for preparative synthesis.

Encouraged by Kishi's rule, which presents that the stereochemistry isformulated as arising from the preferential approach of osmium tetroxideto occur on the face of the olefinic bond opposite to that of thepreexisting hydroxyl or alkoxyl group, dihydroxylations of 41 under theoriginal conditions but without any chiral catalysts, includingSharpless AD catalyst, were conducted. Dihydroxylation of 41 usingKe₃Fe(CN)₆/K₂OsO₂(OH)₄/K₂CO₃ system without chiral catalysts gives theproduct in 77% yield, which product is a 5:1 mixture of isomers with thepredominant isomer being the desired 42. The reaction of olefin 41 withOsO₄ using N-methylmorpholine N-oxide (NMO) as the oxidant withoutchiral catalysts gave a 5:1 mixture of 42 and its isomer in 79% yield.Most surprisingly, when t-butylhydroperoxide (TBHP) is used as oxidantin the presence of catalytic amount of OSO₄ in acetone and ammoniumacetate as buffer (the reagent combination was used in the synthesis ofalditols by Masamune and Sharpless (J. Org. Chem, 1982, 47, 1373)), thecrystalline product isolated is the virtually pure desired 42. Thisprocedure is therefore far superior to the OSO₄/NMO and Fe(CN)₆ ³⁻methods. At 10 molar scale, the desired diol 42 is formed exclusively,and is isolated in 87% yield. No contamination by the other isomer wasdetected in this product by vigorous ¹H NMR analyses.

It is well known that in OSO₄ oxidation the intermediate is cyclicosmate V (below) (Criegee, Liebigs Ann. Chem., 1936, 522, 75).cis-Dihydroxylation of olefins with potassium permanganate in alkalinemedia has been known for quite some time (Robinson and Robinson, J.Chem. Soc., 1925, 127, 1628), and this reaction appears to proceedthrough a cyclic ester VI. Thus attempts at permanganate dihydroxylationhave been performed.

Previous reports have indicated that permanganate dihydroxylation ofolefins in acid or neutral conditions causes over-oxidation of theinitial diol products with concomitant production of ketones andcarboxylates. Only in alkaline conditions further oxidation of the diolproducts can be decelerated. As 41 is a carboxylic ester the reactioncannot be done in aqueous alkali. Hazra et al. (J. Chem. Soc. PerkinTrans. I, 1994, 1667) describes successful dihydroxylation of highlysubstituted olefins to the corresponding diols usingtetradecyltrimethylammonium permanganate (TDTAP) in a mixture of t-BuOH,dichloromethane and water in the presence of 0.1 equivalent of KOH.Application of this method to dihydroxylation of 41 results in rapidformation (within 10 minutes at room temperature) of a mixture of 42 andits diastereomer in an 8:1 ratio, which is isolated in 71% yield.Oxidation occurs much faster in similar reactions without KOH, but theyield of 42 is not improved.

Mukaiyama et al. (Chem. Lett., 1983, 173) disclosed dihydroxylation ofolefins with KMnO₄ and 18-crown-6 ether in dichloromethane at −40° C.Attempts at dihydroxylation of 41 under Mukaiyama's conditions but atdifferent temperatures offer a 6:1 mixture of 42 and its diastereomer in50% yield at −40° C. and the same mixture in 94% yield at −10° C.

Surprisingly, in contrast to the teaching of the prior of art whichdiscloses that oxidation of a double bond with KMnO₄ proceeds via diolwherein the resultant diol is rapidly oxidized further without thepresence of base, diol 42 was found to be isolable when thecorresponding 41 is treated with KMnO₄ without added alkali and crownether. In pure t-butanol, oxidation does not proceed even at roomtemperature conditions for two days. Addition of water to the mixturepromotes the reaction. It is found that the more water in the reactionmedia the faster the reaction proceeds with poor selectivity of 42production; the less water the slower the reaction but improvedselectivity. In any case, the yield is rather poor due to furtheroxidation.

Most surprisingly, and in contradiction to the prior art, treatment of41 with KMnO₄ in acetone is found to give a 10:1 mixture in quantitativeyield, the desired 42 being the major component. The stereoselectivityis found to be improved by performing the reaction in a mixture ofacetone and pyridine.

The following Examples are set forth to aid in an understanding of theinvention. This section is not intended to, and should not beinterpreted to, limit in any way the invention set forth in the claimswhich follow thereafter.

EXAMPLES Example 1(2S,3R,4R)-4,5-O-isopropylidene-2,3-O-sulfuryl-2,3,4,5-tetrahydroxy-2-methyl-pentanoicacid ethyl ester (IIIb, R¹═CH₃, R²═H, R³═CH₃)

To a solution of(2S,3R,4R)-4,5-O-isopropylidene-2,3,4,5-tetrahydroxy-2-methyl-pentanoicacid ethyl ester (R¹═CH₃, R²═H, R³═CH₃) (2.0 g, 8.06 mmol) in anhydrousmethylene chloride (40 mL) containing triethyl amine (3.4 mL) was addedat 0° C. thionyl chloride (0.88 mL, 12.08 mmol) dropwise over 10 min.The resulting reaction mixture was stirred at 0° C. for 10 min, dilutedwith cold ether (100 mL), washed with water (50 mL×2) and brine (50mL×2), dried with sodium sulfate, and concentrated to give a residue(IIIa, R¹═CH₃, R²═H, R³═CH₃) which was dissolved inacetonitrile-tetrachloromethane (10:10 mL). To the obtained solution wasadded at room temperature sodium periodate (2.58 g, 12.06 mmol),ruthenium trichloride (16 mg, 0.077 mmol), and water (14 mL)subsequently. The resulting reaction mixture was stirred at roomtemperature for 10 min, diluted ether (100 mL), washed with water (50mL×2), saturated sodium bicarbonate solution (50 mL×2), and brine (50mL×2), dried with sodium sulfate, concentrated, and co-evaporated withtoluene (30 mL×3) to a syrupy residue, the sulfate IIIb (2.23 g, 89%)which was used for the next reaction without further purification. ¹HNMR (CDCl₃) δ (ppm) 5.04 (d, 1H, J=9.6 Hz, H-3), 4.37 (m, 1H, H-4), 4.29(q, 2H, J=7.6 Hz, CH ₂CH₃), 4.17 (dd, 1H, J=5.6, 9.6 Hz, H-5), 4.05 (dd,1H, J=3.2, 9.6 Hz, H-5′), 1.8 (s, 3H, CH₃-2), 1.38 (s, 3H, (CH ₃)₂C),1.32 (t, 3H, J=6.8 Hz, CH₂CH ₃), 1.31 (s, 3H, (CH ₃)₂C).

Example 2 Tetrabutylammonium salt of(2R,3S,4R)-2-fluoro-4,5-O-isopropylidene-2-methyl-3-sulfooxy-3,4,5-trihydroxypentanoicacid ethyl ester (51B, R¹═CH₃, R²═H, R³═CH₃, Nu=F,M⁺=tetrabutylammonium)

Method 1: To a solution of the sulfate IIIb from Example 1 (628 mg, 2.02mmol) in anhydrous tetrahydrofuran was added at 0° C. tetrabutylammoniumfluoride (1M in tetrahydrofuran, dried with 4 Å molecular sieves)dropwise over 5 min. The resulting reaction mixture was stirred at 0° C.for 20 min, another 2 m L of tetrabutylammonium fluoride (1M intetrahydrofuran, dried with 4 Å molecular sieves, 3 mL) was added, andthen the reaction mixture was stirred at 0° C. for 2 hours, thenconcentrated, and purified by silica gel column chromatography (EtOAc)to give to the fluorinated sulfate, as a syrup (350 mg, 38%). ¹H NMR(CDCl₃) δ (ppm) 4.66 (dd, 1H, J=9.6, 25.6 Hz, H-3), 4.48 (dd, 1H, J=5.2,8.8 Hz, H-4), 4.20, 4.07 (2 m, 4H, H-5, OCH ₂CH₃), 3.21 (m, 8H, N(CH₂CH₂CH₂CH₃)₄), 1.69 (d, 3H, J=22.4 Hz, CH₃-2), 1.59 (m, 8H, N(CH₂CH₂CH₂CH₃)₄), 1.39 (m, 8H, CH₂CH₂CH ₂CH₃)₄), 1.27-1.25 (m, 9H, OCH₂CH ₃,(CH ₃)₂C), 0.96 (t, 12H, J=6.8 Hz, CH₂CH₂CH₂CH ₃)₄.

Method 2: To a solution of the cyclic sulfate IIIb (480 mg, 1.55 mmol)in anhydrous tetrahydrofuran was added at 0° C. tetrabutylammoniumfluoride (1M in tetrahydrofuran, neutralized with HF-pyridine, 3.1 mL)dropwise over 5 min. The resulting reaction mixture was stirred for 39hours, concentrated, and purified by silica gel column chromatography(CH₂Cl₂:MeOH=10:1) to the fluorinated sulfate as a syrup (280 mg, 39%).

Example 3 2-Deoxy-2-fluoro-2-C-methyl-D-ribono-γ-lactone (53B, R²═H,R³═CH₃, Nu=F)

A mixture of the product of Example 2(170 mg, 0.370 mmol),trifluoroacetic acid (0.8 mL), and water (2 mL) in acetonitrile (10 mL)was heated at 80° C. for 1.5 hours, diluted with ethyl acetate (15 mL),washed with water (10 mL) and saturated sodium bicarbonate solution (10mL). The aqueous layer was saturated with NaCl and extracted with ethylacetate (10 mL). The combined organic layer was dried with sodiumsulfate, filtered, and concentrated to give a residue, which waspurified by silica gel column chromatography (hexanes:ethyl acetate=1:1to CH₂Cl₂:MeOH=20:1) to give the desired compound as a white solid (60mg, 100%). ¹H NMR (CDCl₃) δ (ppm) 6.06 (d, 1H, J=6.8 Hz, HO-3), 5.16 (t,1H, J=4.8 Hz, HO-5), 4.26 (m, 1H, H-4), 3.98 (ddd, 1H, J=7.2, 8.0, 23.2Hz, H-3), 3.78 (ddd, 1H, J=2.0, 5.2, 12.8 Hz, H-5), 3.55 (ddd, 1H,J=4.4, 5.6, 12.4 Hz, H-5′), 1.48 (d, 3H, J=24 Hz, CH₃-2); ¹³C NMR(CDCl₃) δ (ppm) 171.2 (d, J=21.2 Hz, C-1), 92.5 (d, J=177.5 Hz, C-2),83.37 (C-4), 70.2 (d, J=15.9 Hz, C-3), 59.0 (C-5), 17.1 (d, J=25.0 Hz,CH₃—C-2).

Example 43,5-Di-O-benzoyl-2-deoxy-2-fluoro-2-C-methyl-D-ribono-γ-lactone (49B,R²═H, R³═CH₃, R⁵=Bz, R⁶=Bz, Nu=F)

The compound of Example 3 (60 mg, 0.16 mmol) was dissolved in anhydrouspyridine (1 mL) and benzoyl chloride (0.3 mL) was added. The resultingreaction mixture was stirred at room temperature for 20 min, water added(1 mL), stirred for 20 min, diluted with ethyl acetate (5 mL), washedwith water (2 mL) and 1M HCl (2 mL×3), and dried with sodium sulfate.Upon filtration and concentration, the residue was purified by silicagel column chromatography (hexanes:ethyl acetate=10:1) to give3,5-di-O-benzoyl-2-deoxy-2-fluoro-D-ribono-γ-lactone as a white solid(118 mg, 87%). ¹H NMR (CDCl₃) δ (ppm) 8.08 (m, 2H, aromatic), 7.99 (m,2H, aromatic), 7.63 (m, 1H, aromatic), 7.58 (m, 1H, aromatic), 7.49 (m,2H, aromatic), 7.43 (m, 2H, aromatic), 5.51 (dd, 1H, J=7.2, 17.6 Hz,H-3), 5.00 (m, 1H, H-4), 4.78 (dd, 1H, J=3.6, 12.8 Hz, H-5), 4.59 (dd,1H, J=5.2, 12.8 Hz, H-5′), 1.75 (d, 3H, J=23.6 Hz, CH₃-2)

Example 5 Tetraethylammonium salt of(2R,3S,4R)-4,5-dihydroxy-2-fluoro-4,5-O-isopropylidene-2-methyl-3-sulfooxy-pentanoicacid ethyl ester (51B, R¹═CH₃, R²═H, R³═CH₃, Nu=F,M⁺=tetraethylammonium)

Method 1. To a solution of the sulfate IIIb (Scheme 9) (1.96 g, 6.32mmol) in anhydrous N,N-dimethylformamide (20 mL) was added at 0° C.tetraethylammonium fluoride hydrate (1.39 g, 9.13 mmol) in one portion.The resulting reaction mixture was stirred for 30 min, concentrated, andco-evaporated with toluene to give a semi-solid (51b) (3.35 g, crude,proton NMR showed virtually one product). ¹H NMR (CDCl₃) δ (ppm) 4.61(dd, 1H, J=9.2, 25.6 Hz, H-3), 4.51 (dd, 1H, J=5.2, 9.2 Hz, H-4),4.23-4.05 (m, 4H, H-5, OCH ₂CH₃), 3.32 (q, 8H, J=7.2 Hz, N(CH ₂CH₃)₄),1.69 (d, 3H, J=23.2 Hz, CH₃-2), 1.31-1.24 (m, 21H, OCH₂CH ₃, (CH ₃)₂C,N(CH₂CH ₃)₄.

Method 2: To a solution of the sulfate IIIb (148 mg, 0.477 mmol) inanhydrous acetonitrile (2 mL) was added at 0° C. tetraethylammoniumfluoride hydrate (107 mg, 0.717 mmol) in one portion. The resultingreaction mixture was stirred for 24 hours, concentrated, andco-evaporated with toluene to give a semi-solid (257 mg, crude, protonNMR showed virtually one product).

Example 6 Preparation of1-(2-deoxy-2-fluoro-2-methyl-3,5-O-3,5dipivaloyl-ribofuranosyly-N⁴-benzoylcytosine(11b, R⁵═R⁶ pivaloyl, R²═H, R³=Me)

To a solution of 49B, (Scheme 6) (Nu=F, R²—H, R³=Me, R⁵═R⁶=pivaloyl,3.44 g, 10.36 mmol) in THF (70 mL) was added LiAl(t-BuO)₃H (13.47 mmol,1M in THF, 13.47 mL) at −20° C. to −10° C. and the resulting solutionwas stirred at −10° C. to −15° C. for 2 h. To the solution was added anadditional LiAl (t-BuO)₃H (1.35 mL, 1.35 mmol) and the solution wasstirred at −10° C. for 1 h. Ice water (50 mL) was added. The mixture wasextracted with EtOAc (200 mL), and the organic layer was washed withwater, brine and dried (Na₂SO₄). Solvent was removed to give crudelactol which was dissolved in CH₂Cl₂ (50 mL). To the solution were addedEt₃N (31.08 mmol, 4.24 mL), 4-dimethylaminopyridine (1 mmol, 122 mg) andtrimethylacetyl chloride (20.7 mmol, 2.55 mL), and the mixture wasstirred at room temperature for 16 h. Water (20 mL) was added, and theresulting mixture was stirred at room temperature for 10 min. EtOAc (200mL) was added, and organic solution was washed with water, brine, anddried (Na₂SO₄). Solvent was removed and the residue was co-evaporatedwith toluene (2×20 mL) to give a crude intermediate (5, 6.74 g) for thenext coupling reaction without purification.

A suspension of N⁴-benzoylcytosine (6.06 mmol, 1.30 g) and (NH₄)₂SO₄ (30mmg) in HMDS (16.7 mL) was refluxed for 5 h, and the clear solution wasconcentrated to dryness under reduced pressure. The residue wasdissolved in 1,2-dichloroethane (50 mL). To the solution were addedcrude 54 (1.96 g, Scheme 6) and SnCl₄ (1.42 mL, 12.12 mmol) at roomtemperature. The solution was refluxed for 24 h. and cooled to 0° C. Tothe solution were added NaHCO₃ (6.11 g, 72.72 mmol) and EtOAc (50 mL).To the mixture was added H₂O (2 mL) slowly, and the resulting mixturewas stirred at room temperature for 20 min. Solid was removed byfiltration. The organic solution was washed with water, brine and dried(Na₂SO₄). Solvent was removed to give syrup as crude mixture ofβ/α-anomers with a ratio of 4/1 in favor to β-isomer. The crude productwas dissolved in MeOH (1 mL) at 50° C. To the solution was added hexanes(10 mL). The mixture was allowed to stay at room temperature for 1 h,then 0° C. for 2 h. Crystals were collected by filtration, washed withhexanes to give product 55, Scheme 6 (323 mg, 20.3% from 49). Motherliquor was concentrated to dryness and purified by column chromatography(20-50% EtOAc in hexanes) to give second crop of 55. H-NMR (CDCl₃): δ8.82 (br s, 1H, NH), 8.10, 7.89, 7.62, 7.52 (m, 7H, H-5, H-6, 5 Ph-H),6.41 (d, J=18.4 Hz, 1H, H-1′), 5.10 (m, 1H, H-3′), 4.45 (d, J=9.6 Hz,1H, H-4′), 4.36 (t, J=2.8 Hz, 2H, H-5′), 1.35 (d, J=22.0 Hz, 3H, Me),1.29, 1.23 [ss, 18H, C(Me)₃].

Example 7(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]-dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) 4-Methylmorpholine N-Oxide as Oxidant with OsmiumCatalyst

To a stirred solution of compound 41 (214 mg, 0.1 mmol) in t-BuOH underargon was added a solution of 4-methylmorpholine N-oxide (0.47 mL, 50 wt% solution in H₂O) and water (0.2 mL). A 2.5 wt % solution of osmiumtetraoxide in tert-butyl alcohol (0.51 mL) is added, and the mixture isstirred for 5 h at room temperature in a water bath. The mixture isevaporated in vacuo to a syrup, which is azeotroped with H₂O (3×10 mL)to remove 4-methylmorpholine. The residue is dried by addition andevaporation of EtOH (2×10 mL) to give a residue, which was purified bysilica gel column chromatography with 20% EtOAc in hexanes to providethe desired product and its isomer (196 mg, 79%) as a solid. Proton NMRindicates that the ratio of the desired product to its isomer is around5:1. Recrystallization of the mixture from hexanes/ethyl acetate givespure product (91 mg, 37.4% from starting material) as a crystallinesolid. ¹H NMR (DMSO-d₆) δ 1.18 (t, J=7.2 Hz, 3H, —OCH₂ CH ₃), 1.24 (s,3H, CH₃), 1.25 (s, 3H, CH₃), 1.28 (s, 3H, 2-CH₃), 3.67 (t, J=7.2 Hz,1H), 3.85, 4.06 and 4.12 (m, 4H), 4.97 (s, 1H, 2-OH, D₂O exchangeable),5.14 (d, J=7.6 Hz, 2-OH, D₂O exchangeable).

Example 8(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Ferricyanide as Oxidant with OsmiumCatalyst

A 100 mL round-bottomed flask, equipped with a magnetic stirrer, ischarged with 5 mL of tert-butyl alcohol, 5 mL of water, and a mixture ofK₃Fe(CN)₆ (0.98 g), K₂CO₃ (0.41 g), and K₂OsO₂(OH)₄ (3.2 mg). Stirringat room temperature produced two clear phases; the lower aqueous phaseappears bright yellow. Methanesulfonamide (95 mg) is added at thispoint. The mixture is cooled to 0° C. whereupon some of saltsprecipitate out, 214 mg (1 mmol) of the compound 41 is added at once,and the heterogeneous slurry is stirred vigorously at 0° C. for 24 h. Tothe mixture is added solid sodium sulfite (1.5 g) while stirring at 0°C., and then the mixture is allowed to warm to room temperature andstirred for 30-60 min. Ethyl acetate (10 mL) is added, and afterseparation of the layers, the aqueous phase is further extracted withEtOAc. The organic layer is dried over Na₂SO₄ and concentrated todryness. The residue is purified by silica gel column chromatographywith 20% EtOAc in hexanes to provide the product (190 mg, 77%) as asolid, proton NMR indicates that the ratio of the desired product to itsisomer is around 5:1. Recrystallization of the mixture withhexanes/ethyl acetate gave pure diol product (102 mg, 41% from startingmaterial) as a crystalline solid. The ¹H NMR spectrum of this product isidentical to that of an authentic specimen.

Example 9(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) t-Butylhydroperoxide as Oxidant at RoomTemperature with Osmium Catalyst

A 50 mL of flask, equipped with magnetic stirrer, is charged with 2 mLof acetone, 214 mg (1 mmol) of compound 41, 65 mg of Et₄NOAc.4H₂O, and0.3 mL of tert-butyl hydroperoxide (5˜6 M in decane). After stirring atroom temperature until the Et₄NOAc a clear solution is obtained, theresulting solution is cooled in an ice bath and 5 mL of OSO₄ (2.5 wt %in t-BuOH) is added in one portion. The solution immediately becomesbrownish purple. After 1 h the ice bath is removed and the reactionmixture is allowed to warm to room temperature and stirred for 14 h. Therest of the procedure is done exactly the same way as described above.After flash column chromatography, 178 mg (72%) of product is obtainedas a solid. In an expanded ¹H NMR, a tiny bump is observed at δ 1.26indicating the presence of an isomer in less than 4% in the product.

Example 10(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) t-Butyhydroperoxide as Oxidant at 0° C. withOsmium Catalyst

A 250 mL of flask, equipped with magnetic stirrer, is charged with 20 mLof acetone, 2.14 g (10 mmol) of compound 41, 650 mg of Et₄NOAc.₄H₂O, and3 mL of tert-butyl hydroperoxide (5˜6 M in decane). After stirring atroom temperature until the Et₄NOAc has dissolved, the resulting solutionis cooled in an ice bath and 5 mL of OsO₄ (2.5 wt % in t-BuOH) is addedin one portion. The solution immediately becomes brownish purple. Thereaction mixture is then stirred at 0° C. for 6.5 h (monitored by TLC,hexanes:ethyl acetate=4:1, Rf=0.18). Ether (40 mL) is added at 0° C. andthe resulting mixture is treated with 5 mL of freshly prepared 10%NaHSO₃ solution in one portion. The ice bath is removed and stirring iscontinued for 1 h. EtOAc (100 mL) and H₂O (50 mL) are added to themixture. After separation of the layers, the aqueous phase is furtherextracted with EtOAc. The organic layer is washed with brine, dried(MgSO₄) and concentrated. The residue is purified by a flash silica gelcolumn chromatography with 20% EtOAc in hexanes to provide the product(2.16 g, 87%) as a solid. No contamination of an isomer is detected inthis product by vigorous ¹H NMR analyses.

Example 11(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Tetradecyltimethylammonium Permanganate (TDTAP) asOxidant

To a stirred solution of compound 41 (214 mg, 1 mmol), in t-BuOH (10 mL)and CH₂Cl₂ (2 mL) at room temperature is added a solution of KOH (6 mg,0.1 mmol) in water followed by TDTAP (0.420 g, 1.12 mmol) in smallportions over a period of five minutes. TLC after 5 minutes showed thatthe reaction is complete. The solution is quenched by using 10 mL ofsaturated sodium bisulfite. The reaction mixture is concentrated invacuo and the residue extracted with ethyl acetate (3×15 mL), dried(Na₂SO₄), evaporated to give a white solid, which is further dissolvedin 5 mL of CH₂Cl₂, passed it through a plug of silica gel topped withCelite, washed with ethyl acetate (50 ml). The filtrate is dried invacuo to give viscous oil (174 mg 71% yield) as an 8:1 mixture of whichthe predominant isomer is the titled compound.

Example 12(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant with 18-Crown-6ether-A (at −40° C.)

To a solution of compound 41 (214 mg, 1 mmol) in CH₂Cl₂ (10 mL) and18-crown-6-ether (37.5 mg, 0.1 mmol) is added KMnO₄ (158 mg, 1 mmol) inportions at −40° C., and the mixture stirred for 2 h at the sametemperature. During this time the reaction mixture turns to dark brown.After the reaction was complete, mixture is quenched with saturatedsolution of sodium bisulfite (10 mL). The resulting colorless mixture isfiltered through a frit, and extracted the filtrate with ethyl acetate(2×25 ml), dried (Na₂SO₄) and concentrated to give a viscous oilconsisting of 10-20% of unreacted olefin starting material along withthe desired diols and its isomer in a ratio of 6:1 (¹H NMR). Olefinstarting material can be removed by passing through a small pad ofsilica gel using 5% ethyl acetate:hexane. A 6:1 mixture of the desireddiols is eluted from the column with 20% ethyl acetate/hexane, andobtained as a white solid (200 mg˜80%) upon evaporation of the solvent.

Example 13(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant with 18-Crown-6ether-B (at −10° C.)

To a solution of compound 41 (214 mg, 1 mmol) in CH₂Cl₂ (10 ml) is added37.5 mg (0.1 mmol) of 18-crown-6-ether, and mixture is cooled to −10° C.KMnO₄ (237 mg, 1.5 mmol) is added in portions, and the mixture stirredat −10° C. for 2 h. During this time the reaction mixture turns to darkbrown, which is treated with saturated solution of sodium bisulfite (10mL). The resulting mixture is filtered through a frit, and the filtrateis extracted with ethyl acetate (2×25 ml), dried (Na₂SO₄) and evaporatedto give a white solid (240 mg, 94.4%) consisting of the desired productand its isomer in a ratio of 6:1.

Example 14(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant in 1:9H₂O/t-BuOH

To a solution of compound 41 (214 mg, 1 mmol) in t-BuOH (9 mL) and H₂O(1 mL) at 0° C. is added KMnO₄ (237 mg, 1.5 mmol) in portions and themixture stirred at the same temperature for 2 h. An additional amount(79 mg, 0.5 mmol) of KMnO₄ is charged and the mixture is stirred foranother 30 minutes. After work up as above, 128 mg (50%) of a mixture ofisomers in a ratio of 8:1 is obtained as a white solid in which themajor component is the desired product.

Example 15(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant in 9:1H₂O/t-BuOH

To a solution of compound 41 (214 mg, 1 mmol) in H₂O (9 mL) and t-BuOH(1 mL) at 0° C. is added KMnO₄ (237 mg, 1.5 mmol) in portions andstirred at the same temperature for 30 minutes. During this time themixture turns to dark brown. Saturated solution of sodium bisulfite (10mL) is added to the mixture, which is filtered, and the filtrate isextracted with ethyl acetate (3×25 ml), dried (Na₂SO₄), and concentratedto give a 4:1 mixture of diol isomers as a white solid (128 mg, 50%), inwhich the titled compound is the major component.

Example 16(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant in H2O at 0° C.

A solution of KMnO₄ (158 mg, 1.0 mmol) in H₂O (10 mL) is added tocompound 41 (214 mg, 1 mmol), and the mixture is stirred at 0° C. for 1hour. The reaction mixture is quenched with saturated solution of sodiumbisulfite (10 mL), and the mixture is worked up as above. A white solid(80 mg, 32%) that is obtained is a 4:1 mixture of diol isomers in whichthe titled compound is the predominant component.

Example 17(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant in Acetone

To a solution of compound 41 (214 mg, 1 mmol) in acetone (10 mL) isadded 37.5 mg, 0.1 mmol) and cooled the reaction mixture to 0° C. Tothis cold solution is added KMnO₄ (237 mg, 1.5 mmol) in portions, andthe reaction mixture is stirred for 2 h at the same temperature. Duringthis time the reaction mixture turns to dark brown. The reaction mixtureis quenched with saturated solution of sodium bisulfite (10 ml) wherethe solution becomes colorless. The reaction mixture is extracted withethyl acetate (3×25 ml), dried and evaporated the mixture to give awhite solid (245 mg, 96.4%) in the ratio of 10:1.

Example 18(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) Potassium Permanganate as Oxidant in a Mixture ofAcetone and Pyridine

To a solution of compound 41 (214 mg, 1 mmol) in a mixture of acetone (9mL) and pyridine (1 mL) at 0° C. is added KMnO₄ (158 mg, 1.0 mmol) andstirred at same temperature for 1 hr. After work up of the reactionmixture as above, 164 mg (67%) of white solid which is practically pureproduct. Vigorous ¹H NMR analyses reveal the crude white solid containsabout 6% of the diastereomer of the titled compound.

Example 19(2S,3R)-3-[(4R)-2,2-Dimethyl-[1,3]dioxolan-4-yl]-2,3-dihydroxy-2-methyl-propionicacid ethyl ester (42) in the RuCl₃/CeCl₃/NaIO₄ system

In a 50 mL round-bottomed flask equipped with magnetic stirring bar, amixture of NaIO₄(321 mg, 1.5 mmol) and CeCl₃.7H₂O (37 mg, 0.1 mmol) in0.45 mL of water is stirred and gently heated until a bright yellowsuspension is formed. After cooling to 0° C., EtOAc (1.25 mL) andacetonitrile (1.5 mL) are added and the suspension is stirred for 2minutes. A 0.1 M aqueous solution of RuCl₃ (25 μL) is added and themixture is stirred for 2 minutes. A solution of the compound 41, (214mg, 1 mmol) in EtOAc (0.25 mL) is added in one portion and the resultingslurry is stirred at 0° C. for 1 hour. Solid Na₂SO₄ (0.5 g) is addedfollowed by EtOAc (3 mL). The solid is filtered off, and the filter cakeis washed several times with EtOAc. Then the filtrate is washed withsaturated Na₂SO₃ solution and the organic layer is dried (Na₂SO₄) andconcentrated to dryness. The residue is purified by silica gel columnchromatography with 20% EtOAc in hexanes to provide a syrup (150 mg,60%). ¹H NMR indicates that the ratio of the desired product to itsisomer is approximately 1.6:1.

Example 20 Reduction and Acylation of compound 49

To a solution of3,5-dibenzoyl-2-fluoro-2-deoxy-2-methyl-D-ribono-lactone (49, 23 g,61.77 mmol, scheme 6) in anhydrous THF (400 ml) was added LiAl(^(t)-OBu)₃H (75 mL 1M in THF, 75.0 mmol) over a period of 15 min at −20to −10° C. and the resulting solution was stirred at the sametemperature until all the starting material was consumed. After 5 hours,−10-20% starting material was left, therefore additional 10 mL ofLiAl(t-OBu₃H (10 mmol) was added at the same temperature and stirred foran hour when TLC indicated all starting material was consumed. To thisreaction mixture were added DMAP (7.5 g) and Ac₂O (58.2 g, 616 mmol) andthe solution was stirred at −10° C. for ˜2-3 h. Upon completion ofreaction (as indicated by TLC) the reaction mixture was diluted withethyl acetate (400 ml) and 200 ml of water. The organic layer wasseparated and the aqueous layer was washed with ethyl acetate (2×100ml). The combined organic layer was washed with water (3×150 ml), brineand dried over anhy. Na₂SO₄. The solvent was removed under reducedpressure and coevaporated with toluene (2×100 mL) to give crude acetateas a clear brown oil. This oil was passed through a plug of silica gel(50 g) and washed with 20% ethyl acetate/hexanes until all the acetatewas recovered. The solvent was evaporated under reduced pressure to givethe desired acetate (54, 32 g) as a colorless oil.

Example 211-(2-deoxy-2-fluoro-2-methyl-3-5-O-dibenzoyl-β-D-ribofuranosyl)-N4-benzoylcytosine(55)

To a suspension of N⁴-benzoylcytosine (20.39 g, 94.74 mmol) in 400 ml ofHMDS was added (NH₄)₂SO₄ (250 mg) and heated under reflux for 4 h.Excess HMDS was removed under reduced pressure. The oily residue wasdissolved in chlorobenzene (1 L). To this solution were added a solutionof the acetate (25 g) in chlorobenzene (250 mL) and SnCl₄ (190.4 mmol,49 g) and the mixture was stirred at room temperature for 2 h followedby heating at ˜65° C. for 16 h. The reaction mixture was cooled to 0° C.to which NaHCO₃ (96 g, 1.14 mol) and ethyl acetate (500 ml) were addedfollowed by careful addition of water (20 ml). This mixture was allowedto stir at room temperature for 30 min. The mixture was filtered undervacuum, the residue washed with ethyl acetate. The organic layer waswashed with water, brine (2×250 mL) and dried over anhydrous Na₂SO₄.Solvent was removed under reduced pressure to give a paleyellowish-brown solid. This was dissolved in MeOH (250 mL) heated underreflux for 30 minutes, cooled to room temperature and filtered, to givethe desired product (55, 8.0 g) as a off-white solid.

Example 22 1-(2-deoxy-2-fluoro-2-C-methyl-β-D-ribofuranosyl)cytosine(14)

A suspension of 55 from Example 21 (16.7 g, 30.8 mmol, scheme 6) wastreated with methanolic ammonia (750 mL, 7M in MeOH) and stirred at roomtemperature for 12 h and concentrated to dryness under reduced pressureto give pale yellow solid. THF (400 mL) was added to the solid andheated under reflux for 30 minutes and cooled to room temperature. Thesolid formed was collected by filtration and washed with THF to give 14(6.7 g, 88%) as an off-white powder.

1. A compound of formula

wherein R′ and R″ are independently H, lower alkyl (C₁-C₆), aryl (C₆-C₂₀), optionally substituted benzyl, trialkylsilyl, t-butyl-dialkylsilyl, t-butyldiphenylsilyl, TIPDS, THP, MOM, MEM, acetyl, benzoyl, or optionally substituted acyl; or R′ and R″ form a cyclopentyl or cyclohexanyl group; R¹ and R² are independently H, lower alkyl (C₁-C₆), aryl (C₆-C₂₀), hydroxymethyl, methoxymethyl, halomethyl, optionally substituted ethenyl, halovinyl, optionally substituted ethynyl, or optionally substituted allyl; and R³ is H, aryl, arylalkyl, or lower alkyl (C₁-C₆).
 2. The compound of claim 1, wherein R′ and R″ are independently H or lower alkyl (C₁-C₆); R¹ and R² are independently H, or lower alkyl (C₁-C₆); and R³ is H or lower alkyl (C₁-C₆).
 3. A compound of formula

wherein each R¹ is independently lower alkyl (C₁-C₆), optionally substituted phenyl, or optionally substituted benzyl; or R¹ forms a cyclopentyl or cyclohexanyl group; R² and R³ are independently hydrogen, lower alkyl (C₁-C₆), hydroxymethyl, methoxymethyl, halomethyl, optionally substituted ethenyl, halovinyl, optionally substituted ethynyl, or optionally substituted allyl; and R⁴ is independently arylalkyl, or lower alkyl (C₁-C₁₀).
 4. The compound of claim 3, wherein each R¹ is independently lower alkyl (C₁-C₆); R² and R³ are independently hydrogen, or lower alkyl (C₁-C₆); and R⁴ is independently lower alkyl (C₁-C₁₀).
 5. The compound of claim 3, having the formula


6. A compound of formula

wherein R² and R³ are independently H, alkyl (C₁-C₁₀), hydroxymethyl, methoxymethyl, halomethyl, optionally substituted ethenyl, halovinyl, optionally substituted ethynyl, or optionally substituted allyl; R⁵ and R⁶ are methoxymethyl, methoxyethyl, benzyloxymethyl, ethoxymethyl, trityl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl, acetyl, pivaloyl, benzoyl, toluoyl, 4-phenyl benzoyl, 2-nitrobenzoyl, 3-nitrobenzoyl, 4-nitrobenzoyl, 2-chlorobenzoyl, 3-chlorobenzoyl, 4-chlorobenzoyl, or substituted benzoyl; Nu is F, Cl, Br, N₃, CN, NO₃, SCN, OR or NR₂ wherein R is acyl or lower alkyl (C₁-C₁₀); and L is a leaving group.
 7. The compound of claim 6, wherein R² and R³ are independently H, alkyl (C₁-C₁₀), or halomethyl; R⁵ and R⁶ are benzoyl; Nu is F; and L is OAc.
 8. The compound of claim 7, wherein R² is H and R³ is methyl.
 9. A compound of formula


10. A compound of formula IIIa, IIIb or IIIc

wherein each R¹ is independently lower alkyl (C₁-C₆), optionally substituted phenyl, or optionally substituted benzyl; R² and R³ are independently hydrogen, lower alkyl (C₁-C₆), hydroxymethyl, methoxymethyl, halomethyl, optionally substituted ethenyl, optionally substituted ethynyl, or optionally substituted allyl; and R⁴ is independently hydrogen, aryl, arylalkyl, or lower alkyl (C₁-C₁₀).
 11. The compound of claim 10, wherein each R¹ is lower alkyl (C₁-C₆); R² and R³ are independently hydrogen, or lower alkyl (C₁-C₆); and R⁴ is lower alkyl (C₁-C₁₀).
 12. The compound of claim 10, having the formula 